Amino acid analogs for tumor imaging

ABSTRACT

The invention provides novel amino acid compounds of use in detecting and evaluating brain and body tumors. These compounds combine the advantageous properties of 1-amino-cycloalkyl-1-carboxylic acids, namely, their rapid uptake and prolonged retention in tumors with the properties of halogen substituents, including certain useful halogen isotopes including fluorine-18, iodine-123, iodine-125, iodine-131, bromine-75, bromine-76, bromine-77 and bromine-82. 
     In one aspect, the invention features amino acid compounds that have a high specificity for target sites when administered to a subject in vivo. Preferred amino acid compounds show a target to non-target ratio of at least 5:1, are stable in vivo and substantially localized to target within 1 hour after administration. An especially preferred amino acid compound is   18  F!-1-amino-3-fluorocyclobutane-1-carboxylic acid (FACBC). 
     In another aspect, the invention features pharmaceutical compositions comprised of an α-amino acid moiety attached to either a four, five, or a six member carbon-chain ring. In addition, the invention features analogs of α-aminoisobutyric acid.

The U.S. Government has certain rights in this invention, based uponpartial support provided by Department of Energy Grant No.DE-FG05-93ER61737.

FIELD OF THE INVENTION

The invention includes novel chemical compounds having specific bindingin a biological system and capable of being used for positron emissiontomography (PET) and single photon emission (SPECT) imaging methods.

BACKGROUND OF THE INVENTION

The ability of analog compounds to bind to localized ligands within thebody would make it possible, in principle, to utilize such compounds forin situ imaging of the ligands by PET, SPECT and similar imagingmethods. In principle, nothing need be known about the nature of theligand, as long as binding occurs, and such binding is specific for aclass of cells, organs, tissues or receptors of interest. PET imaging isaccomplished with the aid of tracer compounds labeled with apositron-emitting isotope (Goodman, M. M. Clinical Positron EmissionTomography, Mosby Yearbook, 1992, K. F. Hubner et al., Chapter 14). Formost biological materials, suitable isotopes are few. The carbonisotope, ¹¹ C!, has been used for PET, but its short half-life of 20.5minutes limits its usefulness to compounds that can be synthesized andpurified quickly, and to facilities that are proximate to a cyclotronwhere the precursor ¹¹ C! starting material is generated. Other isotopeshave even shorter half-lives. ¹³ N! has a half-life of 10 minutes and ¹⁵O! has an even shorter half-life of 2 minutes. The emissions of both aremore energetic than those of ¹¹ C!. Nevertheless, PET studies have beencarried out with these isotopes (Hubner, K. F., in Clinical PositronEmission Tomography, Mosby Year Book, 1992, K. F. Hubner, et al.,Chapter 2). A more useful isotope, ¹⁸ F!, has a half-life of 110minutes. This allows sufficient time for incorporation into aradio-labeled tracer, for purification and for administration into ahuman or animal subject. In addition, facilities more remote from acyclotron, up to about a 200 mile radius, can make use of ¹⁸ F! labeledcompounds. Disadvantages of ¹⁸ F! are the relative scarcity offluorinated analogs that have functional equivalence tonaturally-occurring biological materials, and the difficulty ofdesigning methods of synthesis that efficiently utilize the startingmaterial generated in the cyclotron. Such starting material can beeither fluoride ion or fluorine gas. In the latter case only onefluorine atom of the bimolecular gas is actually a radionuclide, so thegas is designated ¹⁸ F-F. Reactions using ¹⁸ F-F as starting materialtherefore yield products having only one half the radionuclide abundanceof reactions utilizing K¹⁸ F as starting material. On the other hand, ¹⁸F! can be prepared in curie quantities as fluoride ion for incorporationinto a radiopharmaceutical compound in high specific activity,theoretically 1.7 Ci/nmol using carrier-free nucleophilic substitutionreactions. The energy emission of ¹⁸ F! is 0.635 MeV, resulting in arelatively short, 2.4 mm average positron range in tissue, permittinghigh resolution PET images.

SPECT imaging employs isotope tracers that emit high energy photons(γ-emitters). The range of useful isotopes is greater than for PET, butSPECT provides lower three-dimensional resolution. Nevertheless, SPECTis widely used to obtain clinically significant information about analogbinding, localization and clearance rates. A useful isotope for SPECTimaging is ¹²³ I!, a γ-emitter with a 13.3 hour half life. Compoundslabeled with ¹²³ I! can be shipped up to about 1000 miles from themanufacturing site, or the isotope itself can be transported for on-sitesynthesis. Eighty-five percent of the isotope's emissions are 159 KeVphotons, which is readily measured by SPECT instrumentation currently inuse.

Use of ¹⁸ F! labeled compounds in PET has been limited to a few analogcompounds. Most notably, ¹⁸ F!-fluorodeoxyglucose has been widely usedin studies of glucose metabolism and localization of glucose uptakeassociated with brain activity. ¹⁸ F!-L-fluorodopa and other dopaminereceptor analogs have also been used in mapping dopamine receptordistribution.

Other halogen isotopes can serve for PET or SPECT imaging, or forconventional tracer labelling. These include ⁷⁵ Br, ⁷⁶ Br, ⁷⁷ Br and ⁸²Br as having usable half-lives and emission characteristics. In general,the chemical means exist to substitute any halogen moiety for thedescribed isotopes. Therefore, the biochemical or physiologicalactivities of any halogenated homolog of the described compounds are nowavailable for use by those skilled in the art, including stable isotopehalogen homologs.

Numerous studies have demonstrated increased incorporation ofcarbohydrates and amino acids into malignant tumor cells. Thisaccumulation is associated with accelerated proliferation and proteinsynthesis of such cells. The glucose analog ¹⁸F!-2-fluoro-2-deoxy-D-glucose (2-FDG) has been used for distinguishinghighly malignant brain tumors from normal brain tissue or benign growths(DiChiro, G. et al. (1982) Neurology (NY) 32:1323-1329. However,fluorine-18 labeled 2-FDG is not the agent of choice for detecting lowgrade brain tumors because high uptake in normal tissue can mask thepresence of a tumor. In addition, fluorine-18 labeled 2-FDG is not theideal radiopharmaceutical for distinguishing lung tumors from infectioustissue or detecting ovarian carcinoma because of high uptake of the2-FDG radioactivity in infectious tissue and in the bladder,respectively. The naturally occurring amino acid methionine, labeledwith carbon-11, has also been used to distinguish malignant tissue fromnormal tissue. But it too has relatively high uptake in normal tissue.Moreover, the half-life of carbon-11 is only 20 minutes, therefore ¹¹ C!methionine can not be stored for a long period of time.

In an article titled, "1-Aminocyclobutane ¹¹ C! carboxylic Acid, aPotential Tumor-Seeking Agent," published in J. Nucl. Med.20:1055-1061(1979), L. C. Washburn et al. reported that the unnatural, alicyclicα-amino acid, 1-aminocyclobutanecarboxylic acid (ACBC), labeled withcarbon-14 or carbon-11, was incorporated preferentially by several tumortypes in animals. ACBC has been shown to be a selective substrate forprotein synthesis in metastatic lesions in the brain with littleobservable uptake in normal brain tissue.

1-Amino-1-cyclobutane carboxylic acid is also a selective and potentligand and antagonist for the excitatory amino acid receptor subtypeN-methyl-D-aspartic acid (NMDA), specifically the strychnine-insensitiveglycine recognition site. The NMDA receptor has been implicated in CNSdisorders such as epilepsy, stroke, Huntington's disease, Alzheimer'sdisease and schizophrenia.

Synthesis of ACBC has been carried out by the well-knownBucherer-Streker synthesis which is suitable for labeling with ¹¹ C!using ¹¹ C!-cyanide as precursor. (Washburn, L. C. et al., inRadiopharmaceuticals II: Proceedings 2nd International Symposium onRadiopharmaceuticals, Mar. 19-22, 1979, Seattle, Wash.)

SUMMARY OF THE INVENTION

The invention provides novel amino acid compounds of use in detectingand evaluating brain and body tumors. These compounds combine theadvantageous properties of 1-amino-cycloalkyl-1-carboxylic acids,namely, their rapid uptake and prolonged retention in tumors with theproperties of halogen substituents, including certain useful halogenisotopes including fluorine-18, iodine-123, iodine-125, iodine-131,bromine-75, bromine-76, bromine-77 and bromine-82.

In one aspect, the invention features amino acid compounds that have ahigh specificity for target sites when administered to a subject invivo. Preferred amino acid compounds show a target to non-target ratioof at least 5:1, are stable in vivo and substantially localized totarget within 1 hour after administration. An especially preferred aminoacid compound is ¹⁸ F!-1-amino-3-fluorocyclobutane-1-carboxylic acid(FACBC).

In another aspect, the invention features pharmaceutical compositionscomprised of an α-amino acid moiety attached to either a four, five, ora six member carbon-chain ring. In addition, the invention featuresanalogs of α-aminoisobutyric acid.

In a further aspect, the invention features amino acid compounds furthercomprising an imaging agent and uses for the compounds in detectingand/or monitoring tumors in a subject. In one embodiment, the amino acidcompound imaging agent is administered in vivo and monitored using ameans appropriate for the label. Preferred methods for detecting and/ormonitoring an amino acid compound imaging agent in vivo include PositronEmission Tomography (PET) and Single Photon Emission Computer Tomography(SPECT).

Compounds of the invention include fluoro-, bromo- or iodo-substitutedcyclobutyl, cyclopentyl, cyclohexyl amino acids as shown in Scheme 1 orsingly unsaturated cyclic homologs thereof as shown in Scheme 2, ormethylenyl fluoride or iodide-substituted analogs, as shown in Scheme 3,or fluoro- or iodo-substituted isobutyl amino acids as shown in Scheme4. The substituted cyclic compounds of Schemes 1-3 belong to thefollowing generic formula: ##STR1## where R₁ is X, X--CH═CH--, or R₃ R₂is H, or R₃ if R₁ is R₃, ##STR2## such that ##STR3## is formed where xis 0 or 1,

y is 1 or 2,

z is 1, 2, 3 or 4 and z>y if y is 2,

q is 1 or 0 if n is 1 and j is 0,

n is 1 or 2, but 0 if m is 0,

m is 0 or 1,

j is 0 or 1, and

X is F, ¹⁸ F, I, ¹²³ I, ¹²⁵ I, ¹³¹ I, Br, ⁷⁵ Br, ⁷⁶ Br, ⁷⁷ Br, or ⁸² Br.

Non-cyclic, but sterically similar compounds of the invention have thefollowing generic formula, as shown in Scheme 4. ##STR4## where R₁ is Xor X--CH═CH--and x is I, ¹³¹ I, ¹²³ I, ¹²⁵ I, F, ¹⁸ F, Br, ⁷⁵ Br, ⁷⁶ Br,⁷⁷ Br or ⁸² Br.

The compounds of the invention are useful as tumor-binding agents and asNMDA receptor-binding ligands, and in radio-isotopic form are especiallyuseful as tracer compounds for tumor imaging techniques, including PETand SPECT imaging. In order to synthesize the compounds to maximize auseful lifetime for short-lived isotopes, and to maximize yield andpurity, specialized, non-standard routes had to be devised, asdescribed. ##STR5##

DETAILED DESCRIPTION OF THE INVENTION

Compounds of the invention provide substantially improved PET imagingfor areas of the body having malignant tumors, especially tumors of thebrain. All the available positron-emitting isotopes which could beincorporated into a biologically-active compound have short half-lives.The practical utility of such labeled compounds is therefore dependenton how rapidly the labeled compound can be synthesized, the syntheticyield and the radiochemical purity of the final product. Even theshipping time from the isotope source, a cyclotron facility, to thehospital or laboratory where PET imaging is to take place, is limited. Arough calculation of the useful distance is about two miles per minuteof half-life. Thus ¹¹ C!, with a half-life of 20.5 m is restricted toabout a 40 mile radius from a source whereas compounds labeled with ¹⁸F! can be used within about a 200 mile radius. Further requirements ofan ¹⁸ F!-labeled compound are that it have the binding specificity forthe receptor or target molecule it is intended to bind, thatnon-specific binding to other targets be sufficiently low to permitdistinguishing between target and non-target binding, and that the labelbe stable under conditions of the test to avoid exchange with othersubstances in the test environment. More particularly, compounds of theinvention must display adequate binding to the desired target whilefailing to bind to any comparable degree with other tissues or cells.Furthermore, the fluorine, iodine or bromine label must not be labile orunstable such that significant amounts appear in, e.g. bone or thyroid,or other non-taret tissue respectively.

A partial solution to the stringent requirements for PET imaging is toemploy γ-emitting isotopes in SPECT imaging. ¹²³ I! is a commonly usedisotopic marker for SPECT, having a half-life of 13 hours for a usefulrange of over 1000 miles from the site of synthesis. Compounds of theinvention can be rapidly and efficiently labeled with ¹²³ I! for use inSPECT analysis as an alternative to PET imaging. Furthermore, because ofthe fact that the same compound can be labeled with either isotope, itis possible for the first time to compare the results obtained by PETand SPECT using the same tracer.

In vivo distribution of a compound of the invention, ¹⁸F!-1-amino-3-fluoro-cyclobutane-1-carboxylic acid (FACBC) was measuredin rats having an implanted gliosarcoma. Accumulation in various tissuewas measured at 5 min and 60 min post-administration. The compound wasimmediately seen to be preferentially associated with tumor tissue asearly as 5 minutes post administration, with relatively little uptake inother tissues. After 60 minutes, an increased level of tumor uptakerelative to non-malignant brain tissue was observed, with very littleadditional uptake in other tissues. Uptake by bone was essentiallyconstant over the 60 minutes of exposure, indicating stability of the2-cyclobutyl group to significant in vivo defluorination. The tumoruptake exhibited a maximum at 60 minutes of 1.72% of total injecteddose/gram of tissue, with a maximum ratio of tumor to brain of 6.61,compared to 5.58 at 5 minutes. By contrast, ¹⁸ F! fluorodeoxyglycose(FDG) showed rapid accumulation but poor discrimination between tumorand brain, the dose/gram ratio of tumor uptake to brain uptake being0.84 at 60 min. The results with ¹⁸ F!FACBC indicate that the compoundis a valuable imaging agent for diagnosis, management and imaging ofmalignant tumors, using PET imaging.

The specificity of tumor binding also provides utility for I-substitutedcompounds of the invention. Such compounds can be labeled withshort-lived ¹²³ I for SPECT imaging or with longer-lived ¹²⁵ I forlonger-term studies such as monitoring a course of therapy. Other iodineand bromine isotopes can be substituted for those exemplified.

The compounds of the invention therefore provide improved methods fortumor imaging using PET and SPECT. The methods entail administering to asubject (which can be human or animal, for experimental and/ordiagnostic purposes) an image-generating amount of a compound of theinvention, labeled with the appropriate isotope and then measuring thedistribution of the compound by PET if ¹⁸ F! or other positron emitteris employed, or SPECT if ¹²³ I! or other gamma emitter is employed. Animage-generating amount is that amount which is at least able to providean image in a PET or SPECT scanner, taking into account the scanner'sdetection sensitivity and noise level, the age of the isotope, the bodysize of the subject and route of administration, all such variablesbeing exemplary of those known and accounted for by calculations andmeasurements known to those skilled in the art without resort to undueexperimentation.

It will be understood that compounds of the invention can be labeledwith an isotope of any atom or combination of atoms in the structure.While ¹⁸ F!, ¹²³ I! and ¹²⁵ I! have been emphasized herein as beingparticularly useful for PET, SPECT and tracer analysis, other uses arecontemplated including those flowing from physiological orpharmacological properties of stable isotope homologs and will beapparent to those skilled in the art.

EXAMPLE 1

Synthesis of 18F!-1-amino-3-fluoro-cyclobutane-1-carboxylic acid (FACBC)

As will be described in detail hereinafter, the compound can be preparedby the steps represented in Steps 1-11.

The following methods were employed in procedures reported herein. ¹⁸F!-Fluoride was produced from a Seimens cyclotron using the ¹⁸ O(p,n)¹⁸F reaction with 11 MeV protons on 95% enriched ¹⁸ O! water. All solventsand chemicals were analytical grade and were used without furtherpurification. Melting points of compounds were determined in capillarytubes by using a Buchi SP apparatus. Thin-layer chromatographic analysis(TLC) was performed by using 250-mm thick layers of silica gel G PF-254coated on aluminum (obtained from Analtech, Inc.). Column chromatographywas performed by using 60-200 mesh silica gel (Aldrich Co.). Infraredspectra (IR) were recorded on a Beckman 18A spectrophotometer with NaClplates. Proton nuclear magnetic ##STR6## resonance spectra (1H NMR) wereobtained at 300 MHz with a Nicolet high-resolution instrument.

Synthesis of 1-Chloro-2-benzyloxy-3-bromopropane 3:

A mixture of benzyl bromide 1 (46.2 g, 0.27 mol), epichlorohydrin 2 (25g, 0.27 mol), and 0.045 g of mercurous chloride was heated for 12 hr at150° C. (Step 1). Distillation through a 12-in Vigreux column yielded55.8 g (79%) of 1-chloro-2-benzyloxy-3-bromopropane, 3 bp 142-145 (0.3mm); 1H NMR (CDCl₃) δ 3.34-3.9 (m, 4H, CH₂), 4.58 (s, 2H,O--CH₂), 7.26(s, 5H, phenyl).

Synthesis of Diethyl-3-benzyloxy cyclobutane-1-dicarboxylate 4:

To a stirred slurry of 4.6 g (0.19 mol) sodium hydride in 115 mL of drydioxane was added dropwise 30.4 (0.10 mol) of diethyl malonate over a 30min period. After this addition was complete, 50.0 g (0.19 mol) of1-chloro-2-benzyloxy-3-bromopropane 3 was added dropwise in 30 min (Step2). The mixture was heated at reflux for 44 hr, cooled to roomtemperature, and 4.6 g (0.19 mol) of sodium hydride in 50 mL of dioxanewas added in portions. The mixture was heated at reflux for anadditional 120 hr. The solvent was partially removed under reducedpressure and the mixture was treated with 100 mL of water. The organiclayer was extracted into ether. The ether extracts were dried andconcentrated and the residue was distilled under reduced pressure.Distillation through a 12-in Vigreux column yielded 49.0 g (85%) ofdiethyl 3-benzyloxycyclobutane-1,1-dicarboxylate 4 bp 174°-176° C. (0.9mm); ¹ H NMR(CDCl₃) δ 1.23 (t, J=7 Hz, 6H, CH₃), 4.0-4.7 (m, 1H OCH),4.34 (s, 2H OCH₂), 4.13 (q, J=7 Hz, 4H, OCOCH₂), 7.23 (s, 5H, phenyl).

Synthesis of 3-benzyloxycyclobutane-1,1-dicarboxamine 5:

Diethyl 3-benzyloxycyclobutane-1,1-dicarboxylate 4 (20 g. 65 mmol) wasstirred with concentrated aqueous ammonia (250 mL) for four days at roomtemperature (Step 3). The diamide 5 was collected by filtration andwashed with water followed by ethyl acetate. The yield was 8.1 g (50%).¹ H NMR (d6-DMSO) δ 2.2 (m, 2H, CH₂), 2.5 (m, 2H, CH₂), 3.8 (q, J=7.2 Hz1H OCH), 4.3 (s, 2H, OCH₂), 7.0 (m, 4H, NH₂), 7.23 (s, 5H, phenyl).

Synthesis of cis/trans 5-(3-benzyloxycyclobutane)hydantoin 6:

3-Benzyloxycyclobutane-1, 1-dicarboxamine, 5 (2.0 g, 8 mmol) was stirredin 150 mL of dilute sodium hypochlorite (Aldrich product/water 1 to 2)at 0°-5° C. for four hrs (Step 4). The reaction mixture stood overnightat room temperature. Unreacted diamide was recovered by filtration. Thesolution was neutralized to pH 5 with concentrated hydrochloric acid andevaporated to dryness in vacuo. The residue was extracted with 50 mL ofhot methanol, filtered, and washed with 50 mL of hot methanol. Themethanol solutions were combined and evaporated. Yield of the mixture ofcis and trans hydantoins 6 was 1.4 g(70%).

Synthesis of 1-amino-3-benzyloxycyclobutane-1-carboxylic acid 7:

The hydantoin 6 (1.0 g,4.1 mmol) was hydrolyzed by refluxing with 10 mLof a barium hydroxide solution (saturated at room temperature) for 16 hr(Step 5). The solution was neutralized to pH 6 with 2M sulfuric acid andevaporated to dryness in vacuo. The residue was extracted with 50 mL ofhot methanol, filtered, and washed with 50 mL of hot methanol. Themethanol solutions were combined and evaporated. Yield of the1-amino-3-benzyloxycyclobutane-1-carboxylic acid 7 was 0.69 g(76%). ¹ HNMR (d₄ -methanol) δ 2.2-2.9 (m, 4H, CH₂), 4.3 (t, J=6.9 Hz, 1H, OCH),4.5 (s, 2H, OCH₂), 7.23 (br s, 5H, phenyl)

Synthesis of 1-t-butylcarbamate-3-benzyloxycyclobutane-1-carboxylic acid8:

A solution of the amino acid 7 (0.5 g, 2.3 mmol) in 10 mL of a mixtureof methanol/triethylamine (90:10) was treated with 1.0 g (4.6 mmol) ofdi-tert-butyldicarbonate (Step 6). The mixture was heated at 50°-60° C.for 10 min and then the solvent was removed by rotoevaporation. Thecrude product was stirred in 5 mL of dilute HCl (pH=2) at 0° C. for 10min. The mixture was extracted with CH₂ Cl₂ (2×10 mL), the combinedextract dried, and the solvent was removed. The crude oil waschromatographed on silica gel using methylene chloride/methanol (9 to 1)with 0.1% formic acid. The product 8 (0.55 g, 78%) showed a single spoton TLC (Rf=0.59) with the same solvent system; visualization was withMoO.H₃ PO₄.

Synthesis of1-t-butylcarbamate-3-benzyloxycyclobutane-1-carboxylic-methyl ester 9:

To a slurry of 1-methyl-3-nitro-1-nitrosoguandine (150 mg) in 8 mL ofether at 0°-5° C. was added a 40% solution of potassium hydroxidedropwise. The resultant diazomethane ether solution was added to 0.15g(0.50 mmol) of 1-t-butyl carbamate-3-benzyloxycyclobutane-1-carboxylicmethyl ester acid in 3 mL of ether (Step 7) and the mixture was stirredat room temperature for 15 min. The mixture was washed with water (10mL) and the ether evaporated. The crude residue was chromatographed onsilica gel using ethyl acetate/hexane (1 to 9). Yield: 0.13 g (82%); ¹ HNMR (CDCl₃) δ 1.35 (s, 9H, CH₃), 2.27-2.88 (m, 4H, CH₂), 3.72 (s, 3H,CH₃) 4.18 (m, 1H, CHO), 4.42 (s, 2H, OCH₂), 7.23 (br s, 5H, phenyl).

Synthesis of 1-t-butylcarbamate-3-hydroxy-cyclobutane-1-carboxylic acidmethyl ester 10:

A solution of 0.10 g (0.3 mmol) of the protected amino acid benzyl ether9 in 5 mL of methanol was mixed with a suspension of 25 mg of 10%palladium on charcoal in 5 mL of methanol (Step 8). The mixture wasstirred under a positive pressure of hydrogen (balloon) for 16 hr. Thecatalyst was filtered off and the solvent was evaporated. The cruderesidue was chromatographed on silica gel using methylenechloride/methanol (9 to 1). The product 10 (74 mg 89%) showed a singlespot on TLC (Rf=0.81) with the same solvent system; visualization waswith MoO.H₃ PO₄.

Synthesis of 1-t-butylcarbamate-3-trifluoromethanesulfonoxy-cyclobutane-1-carboxylic acid methyl ester 11:

The alcohol 10 (25 mg, 0.10 mmol) was dissolved in 10 mL of drymethylene chloride and pyridine (12 μL) by stirring under N₂. Thesolution was cooled to 0°-5° C. and 12 μL of trifluoromethane sulfonicanhydride was added (Step 9). After 1 hr, the solvent was removed invacuo and the crude oil was chromatographed on silica gel using ethylacetate/hexane (3 to 7). The product 11 (24 mg, 64%) showed a singlespot on TLC (Rf=0.60) with the same solvent system; visualization waswith MoO.H₃ PO₄.

Synthesis of 3- ¹⁸ F!-fluoro-cyclobutane-1-amino-1-carboxylic acid ¹⁸ F!FACBC 13:

¹⁸ F!-Fluoride was produced using the ¹⁸ O(p,n)¹⁸ F reaction with 11 MeVprotons on 95% enriched ¹⁸ O! water. After evaporation of the water anddrying of the fluoride by acetonitrile evaporation, the protected aminoacid triflate 11 (3 mg) was introduced in an acetonitrile solution (1mL). The no carrier added (NCA) fluorination reaction (Step 10) wasperformed at 85° C. for 5 min in a sealed vessel in the presence ofpotassium carbonate and Kryptofix (Trademark Aldrich Chemical Co.,Milwaukee, Wis.). Unreacted ¹⁸ F- was removed by diluting the reactingmixture with methylene chloride followed by passage through a silica gelSeppak which gave the ¹⁸ F labeled product 12 in 42% E.O.B. yield.Deprotection of 12 (Step 11) was achieved by using 1 mL of 4N HCl at115° C. for 15 min and then the aqueous solution containing ¹⁸ FACBC 13was passed through an ion-retardation resin (AG 11A8 50-100 mesh). Thesynthesis was completed in 60 min following E.O.B. with an overallradiochemical yield of 12% (17.5% E.O.B.).

EXAMPLE 2

Synthesis of ¹⁸ F!-2-Amino-3-fluoro-2-methylpropane-1-carboxylic acid 24(FAMPC)

3-Benzyloxy-1,2-epoxypropane 15

Sodium hydride (60% oil dispersion, 23.6 g, 0.59 mol) was added inportions to a solution of glycidol (14) (40 g, 0.54 mol), benzyl bromide(101.5 g, 0.59 mol), and n-butylammonium iodide (0.24 g) in dry DMF (150mL) at 25° C. (Step 12). The mixture was stirred for 1 hr at 65° C.,poured over ice and then extracted with ether (2×75 mL). The combinedether extract was washed with water (3×75 mL) and dried over MgSO₄.Distillation using a 12-in vigreux column afforded 62.9 g (71%) ofglycidyl ##STR7## benzyl ether 15; bp 120°-122° C. (10 mm); ¹ H NMR(CDCl₃) δ 2.6 (dd, 1H, OCHa), 2.8 (dd, 1H, OCHb), 3.2 (m, 1H, OCHc), 3.2(dd, 1H, OCHd), 3.8 (dd, 1H, OCHe), 4.6 (dd, 2H, OCH₂), 7.23 (s, 5H,phenyl).

3-Benzyloxypropan-2-ol 16

To a suspension of lithium aluminum hydride (6.1 g, 0.16 mol) in ether(50 mL) at 25° C. was added a solution of glycidyl benzyl ether 15 (52.9g, 0.32 mol) in 50 mL of ether (Step 13). The mixture was refluxed for 2h and cooled to room temperature. A solution of 1N NaOH was addeddropwise to the mixture and the precipitated metal salts were removed byfiltration. The ether containing the product was washed with water (50mL), dried (MgSO₄) and the solvent removed by roto-evaporation.Distillation gave 43.3 g (82%) of 3-benzyoxypropan-2-ol; 16 bp 110-112(5 mm). ¹ H NMR (CDCl₃) δ 1.13 (d, J=6.6 Hz, 3H, CH₃), 2.5 (br s, 1H,OH), 3.28 (dd, 1H, OCH), 3.45 (dd, 1H, OCH), 4.0 (m, 1H, OCH), 4.55 (s,2H, OCH₂), 7.35 (s, 5H, phenyl).

3-Benzyloxypropan-2-one 17

3-Benzyoxypropan-2-ol 16 (40 g, 0.24 mol) was added to a suspension ofpyridinium chlorochromate (155.2 g, 0.72 mol) in DMF (150 ml) at 25° C.,stirred at 65° C. for 3 h, and then diluted with water (75 mL) (Step14). The mixture was extracted with ether (2×50 mL) and the combinedether layers were washed with water (3×50 mL) dried (MgSO₄) and thesolvent removed by roto-evaporation. Distillation gave 31 g (77%) of3-benzyloxypropan-2-one; 17 bp 104-106 (10 mm). ¹ H NMR (CDCl₃) δ 2.16(s, 3H, CH₃), 4.05 (s, 1H, OH), 4.59 (s, 2H, OCH₂), 7.5 (s, 5H, phenyl).

2-(3-benzyloxypropane)hydantoin 18

3-Benzyloxypropan-2-one 17 (25 g, 0.15 mol) was dissolved in 300 mL of50% ethanol containing ammonium carbonate (68.3 g, 0.60 mol) andpotassium cyanide (19.5 g, 0.30 mol) was added. The mixture was warmedto 60° C. for 2 h and evaporated to dryness in vacuo (Step 15). Theresidue was extracted with 75 mL of hot methanol, filtered, and filtercake washed with 50 mL of hot methanol. The methanol solutions werecombined, solvent evaporated, and the residue chromatographed on silicagel using CH₂ Cl₂ /methanol 90:10. Yield of 3-benzyloxypropan-2-onehydantoin 18 was 23 g (66%). ¹ H NMR (d4-methanol) δ 1.22 (s, 3H, CH₃),3.41 (d, J=9.6 Hz, 1H, OCHa), 3.52 (d, J=9.6 Hz 1H, OCHb), 4.5 (s, 2H,NH), 4.8 (s, 2H, OCH₂), 8.25 (m, 5H, phenyl).

2-Amino-3-benzyloxy-2-methyl-1-propionic acid 19

The hydantoin 18 (6.0 g, 25.6 mmol) was hydrolyzed by refluxing with 20mL of a barium hydroxide solution (saturated at room temperature) for 16hr (Step 16). The solution was neutralized to pH 6 with 2 M sulfuricacid and evaporated to dryness in vacuo. The residue was extracted with50 mL of hot methanol, filtered, and washed with 50 mL of hot methanol.The methanol solutions were combined and evaporated. Yield of the aminoacid 19 was 4.1 g (76%).

2-t-Butyl carbamate-3-benzyloxy-2-methyl-1-propionic acid 20

A solution of the amino acid 19 in 10 mL of a mixture ofmethanol-triethylamine (90:10) is treated with 1.0 g (4.6 mmol) ofdi-tert-butyl dicarbonate (Step 17). The mixture is heated at 50°-60° C.for 10 min and then the solvent removed by roto-evaporation. The crudeproduct is stirred in 5 mL of dilute HCl (pH=2) at 0° C. for 10 min. Themixture is extracted with CH₂ Cl₂ (2×10 mL), the combined extract dried,and the solvent removed.

The crude oil, 20, is chromatographed on Silica gel using methylenechloride/methanol (9 to 1) with 0.1% formic acid.

2-(t-Butyl carbamate)-3-benzyloxy-2-methyl-1-methylpropionate 21

To a slurry of 1-methyl-3-nitro-1-nitrosoguandine in ether at 0°-5° C.is added a 40% solution of potassium hydroxide dropwise. The resultantdiazomethane ether solution is added to 1-t-butylcarbamate-3-benzyloxy-1-methylpropane-1-carboxylic acid 20 in 3 mL ofether and the mixture is stirred at room temperature for 15 min (Step18). The mixture is washed with water (20 mL) and the ether evaporated.The crude residue 21 is chromatographed on silica gel using ethylacetate/hexane (1 to 9).

2-(t-Butyl carbamate)-3-hydroxy-2-methyl-1-propionate 22

A solution of the protected amino acid benzyl ether 21 in 5 mL ofmethanol is mixed with a suspension of 25 mg of 10% palladium oncharcoal in 5 mL of methanol (Step 19). The mixture is stirred under apositive pressure of hydrogen (balloon) for 16 hr. The catalyst isfiltered off and the solvent is evaporated. The crude residue ischromatographed on silica gel using methylene chloride (9 to 1) to yield22.

2-(t-Butyl carbamate)-3-trifluoromethanesulfonoxy-2-methyl-1-methylpropionate 23

The alcohol 22 is dissolved in 10 mL of dry methylene chloride andpyridine (12 μL) by stirring under N₂. The solution is cooled to 0°-5°C. and 12 μL of trifluoromethane sulfonic anhydride is added (Step 20).After 1 hr, the solvent is removed in vacuo and the crude oil ischromatographed on silica gel using ethyl acetate/hexane (3:7) to yield23.

¹⁸ F!-2-Amino-3-fluoro-2-methyl-1-propionic acid 24

¹⁸ F!-Fluoride is produced using the ¹⁸ O(p,n) ¹⁸ F reaction with 11 MeVprotons on 95% enriched ¹⁸ O! water. After evaporation of the water anddrying of the fluoride by acetonitrile evaporation, the protected aminoacid triflate 23 (3 mg) is introduced in a acetonitrile solution (1 mL).The (NCA) fluorination reaction (Step 21) is performed at 85° C. for 5min in a sealed vessel in the presence of potassium carbonate andKryptofix. Unreacted ¹⁸ F⁻ is removed by diluting the reacting mixturewith methylene chloride followed by passage through a silica gel Seppakwhich gives the ¹⁸ F labeled product. Deprotection (Step 22) is achievedby using 1 mL of 4N HCl at 115° C. for 15 min and then the aqueoussolution is passed through an ion-retardation resin (AG 11A8 50-100mesh) to yield 24.

EXAMPLE 3

Synthesis of ¹⁸ F!-1-Amino-3-fluoro-cyclopentane-1-carboxylic acid 37(FACPC)

4-Bromo-1,2-epoxybutane 26

A solution of m-chloroperbenzoic acid (50% pure, 72.5 g, 0.21 mol) in500 mL of methylene chloride was added dropwise to a stirred ice-cooledsolution of 4-bromo-1-butene 25 (25 g, 0.19 mol) in 100 mL of methylenechloride (Step 23). After the addition, the mixture was stirred at 25°C. for 18 h, during which time m-chlorobenzoic acid precipitated. Thereaction mixture was washed with 4N sodium hydroxide until the aqueousphase remained alkaline and with water until neutral. The organic phasewas dried (MgSO₄) and the solvent removed in vacuo to give 27.9 g (89%)of 4-bromo-1,2-epoxybutane 26. ¹ H NMR (CDCl₃) δ 2.10 (m, 2H,O--C--CH₂), 2.58 (d,d J=5.0, 2.6 Hz, 1H, OCHa) 2.82 (dd J=5.0,4.0 Hz),1H, OCHb), 3.09 (m, 2H, O--C--CH₂, 3.55 (t, J=7 Hz, 2H).

Diethyl 3-hydroxycyclopentane-1,1-dicarbonate 27

A solution of diethyl malonate (7.7 g, 48.5 mmol) in 53.4 mL of 1Nethanolic sodium ethoxide was stirred for 15 min in a ice bath, afterwhich 4-bromo-1,2-epoxybutane 26 (14.6 g, 97 mmol) was added (Step 24).After stirring at 25° C. for 3 h, the mixture was poured into water andthe ethanol evaporated in vacuo. The aqueous solution was extracted withchloroform, the extracts dried (MgSO₄) and concentrated. Distillationgave 8.14 g (73%) of product 27; bp 155°-160° C. (0.5 mm); ¹ H NMR(CDCl₃) δ 1.3 (t, J=7.2 Hz, 6H, CH₃), 1.7-2.7 (m, 6H, CH₂), 3.02 (s, 1H,OH), 4.2 (q, J=7.2 Hz, 4H, O═COCH₂), 4.2 (m, 1H, OCH).

Diethyl 3-benzyloxycyclopentane-1,1-dicarboxylate 28

Sodium hydride (60% oil dispersion, 2.1 g, 53 mmol) was added inportions to a solution of diethyl3-hydroxycyclopentane-1,1-dicarboxylate 27 (11 g, 48 mmol), benzylbromide (9.7 g, 53 mol), and n-tetrabutylammonium iodide (100 mg) in dryDMF (50 mL) at 25° C. (Step 25). The mixture was stirred for 1 hr at 65°C., poured onto ice and then extracted with ether (2×50 mL). The##STR8## combined either extract was washed with water (3×50 mL) anddriedover MgSO₄. Chromatography on silica gel (10:90 ethylacetate/hexane, Rf=0.38) afforded 11.6 g (75%) of the benzyl ether 28; ¹H NMR (CDCl₃) δ 1.3 (t, J=7.2 Hz, 6H, CH₃), 1.7-2.7 (m, 6H, CH₂), 4.2(q, J=7.2 Hz, 4H, O═COCH₂), 4.1 (m, 1H, O--CH), 4.6 (s, 2H, O--CH₂), 7.3(s, 5H, phenyl).

3-Benzyloxycyclopentane-1,1-dicarboxamine 29

Diethyl 3-benzyloxycyclopentane-1,1-dicarboxylate 28 (10 g, 31 mmol) isstirred with concentrated aqueous ammonia (100 mL) for four days at roomtemperature (Step 26). The resultant diamide 29 is collected byfiltration and washed with water followed by ethyl acetate.

Cis/trans 5-(3-benzyloxycyclopentane)hydantoin 30

3-Benzyloxycyclopentane-1,1-dicarboxamine 29 is stirred in 150 mL ofdilute sodium hypochlorite (Aldrich product/water 1:2) at 0°-5° C. for 4hr and then allowed to stand overnight at room temperature (Step 26).Unreacted diamide will be recovered by filtration. The solution isneutralized to pH 5 with concentrated hydrochloric acid and evaporatedto dryness in vacuo. The residue is extracted with 50 mL of hotmethanol, filtered, and washed with 50 mL of hot methanol. The methanolsolutions are combined and evaporated.

1-Amino-3-benzyloxycylcopentanecarboxylate acid 31

The hydantoin 30 is hydrolyzed by refluxing with 10 mL of a bariumhydroxide solution (saturated at room temperature) for 16 hr (Step 28).The solution is neutralized to pH 6 with 2 M sulfuric acid andevaporated to dryness in vacuo. The residue is extracted with 50 mL ofhot methanol, filtered, and washed with 50 mL of hot methanol. Themethanol solutions are combined and evaporated.

1-t-Butyl carbamate-3-benzyloxy-1-cyclopentane-1-carboxylic acid 32

A solution of the amino acid 31 in 10 mL of a mixture ofmethanol/triethylamine (90:10) is treated with di-tert-butyl dicarbonate(Step 29). The mixture is heated at 50-60° C. for 10 min and then thesolvent is removed by rotoevaporation. The crude product is stirred in 5mL of dilute HCl (pH=2) at 0° C. for 10 min. The mixture is extractedwith CH₂ Cl₂ (2×10 mL), the combined extract dried, and the solventremoved. The crude oil is chromatographed on silica gel using methylenechloride/methanol (9 to 1) with 0.1% formic acid to yield 32.

1-t-Butyl carbamate-3-benzyloxy-1-cyclopentane-1-carboxylic acid methylester 33

To a slurry of 1-methyl-3-nitro-1-nitrosoguandine in ether at 0°-5° C.will be added to a 40% solution of potassium hydroxide dropwise. Theresultant diazomethane ether solution is added to 1-t-butylcarbamate-3-benzyloxycyclopentane-1-carboxylic acid 32 in 3 mL of etherand the mixture is stirred at room temperature for 15 min (Step 30). Themixture is washed with water (10 mL) and the ether evaporated. The cruderesidue is chromatographed on silica gel using ethyl acetate/hexane (1to 9) to yield 33.

1-t-Butyl carbamate-3-hydroxy-1-cyclopentane-1-carboxylic acid methylester 34

A solution of the protected amino acid benzyl ether 33 in 5 mL ofmethanol is mixed with a suspension of 25 mg of 10% palladium oncharcoal in 5 mL of methanol (Step 31). The mixture is stirred under apositive pressure of hydrogen (balloon) for 16 hr. The catalyst isfiltered off and the solvent is evaporated. The crude residue ischromatographed on silica gel using methylene chloride/methanol (9 to 1)to yield 34.

1-t-Butyl carbamate-3-trifluoromethanesulfonoxy-1-cyclopentane-1-carboxylic carboxylic acid methyl ester 35

The alcohol is dissolved in 10 mL of dry methylene chloride and pyridine(12 μL) by stirring under N₂. The solution is cooled to 0°-5° C. and 12μL of trifluoromethane sulfonic anhydride is added (Step 32). After 1hr, the solvent is removed in vacuo and the crude oil is chromatographedon silica gel using ethyl acetate/hexane (3:7) to yield 35.

¹⁸ F!-1-Amino-3-fluorocyclopentane-1-carboxylic acid 37

¹⁸ F!-Fluoride will be produced using the ¹⁸ O(p,n)¹⁸ F reaction with 11MeV protons on 95% enriched ¹⁸ O! water. After evaporation of the waterand drying of the fluoride by acetonitrile evaporation, the protectedamino acid triflate 35 (3 mg) is introduced in an acetonitrile solution(1 mL). The (NCA) fluorination reaction is performed at 85° C. for 5 minin a sealed vessel in the presence of potassium carbonate and Kryptofix(Step 33). Unreacted ¹⁸ F⁻ is removed by diluting the reacting mixturewith methylene chloride followed by passage through a silica gel Seppakwhich gives the ¹⁸ F labeled product 36. Deprotection (Step 34) isachieved by using 1 mL of 4N HCl at 115° C. for 15 min and then theaqueous solution is passed through an ion-retardation resin (AG 11A850-100 mesh) to yield 37 (FACPC).

EXAMPLE 4

¹⁸ F!-1-Amino-4-fluoro-cyclohexane-1-carboxylic acid 49 (FACHC)

4-Hydroxycyclohexanone ethylene ketal 49

Sodium borohydrate (2.4 g, 64 mmol) was added in portions to a stirredice cold solution of 1,4 cyclohexanedione monoethylene ketal 38 (20 g,128 mmol) in 60 mL of methanol (Step 35). After addition was complete,1N HCl was added to the solution dropwise until a pH of 8 was obtainedand then the solvent was removed by roto-evaporation. The product 39(16.8 g, 84%) showed a single spot on TLC (Rf=0.4, ethyl acetate/hexane20:80 solvent system, visualization was with acidic vanillin ethanolsolution) and was used without further purification. ¹ H NMR (CDCl₃) δ1.6-1.9 (m, 8H, ring-CH₂), 3.8 (m, 1H, CH-O), 4.0 (s, 4H, ketal-CH₂),5.3 (s, 1H, OH).

4-Benzyloxycyclohexanone ethylene ketal 40

Sodium hydride (60% oil dispersion, 2.2 g, 56 mmol) was added inportions to a solution of 6-hydroxycyclohexanone ethylene ketal (39)(8.8 g, 51 mmol), benzyl bromide (9.6 g, 5.6 mmol), andtetra-n-butylammonium iodide (50 mg) in dry DMF (50 mL) at 25° C. (Step36). The mixture was stirred for 1 hr at 65° C., poured over ice andthen extracted with ether (2×50 mL). The combined ether extract was##STR9## washed with water (3×50 mL), dried (MgSO₄) and solvent wasremoved. Chromatography on silica gel using 10:90 ethyl acetate/hexane(Rf=0.39) afforded 8.9 g (70%) of the benzyl ether 40. ¹ H NMR (CDCl₃) δ1.6-1.9 (m, 8H, ring-CH₂), 3.6 (m, 1H, CH--O), 4.0 (2, 4H, ketal--CH₂),4.6 (s, 2H, CH₂ --O).

4-Benzyloxycyclohexanone 41

A solution of 4-benzyloxy cyclohexanone ethylene ketal 40 (5.0 g, 20.1mmol) in methanol (20 mL) and 1N HCl (0.5 mL) was stirred overnight at25° C. (Step 37). The mixture was neutralized by addition of 1N NaHCO₃(0.5 mL), solvent removed by roto-evaporation, and the residuechromatographed on silica gel using 15:85 ethyl acetate/hexane. Yield ofthe ketone 41 was 2.7 g (67%); Rf=0.35; ¹ H NMR (CDCl₃) δ 2.3 (m, 8H,ring--CH₂) 3.6 (m, 1H, CH--O), 4.6 (s, 2H, CH₂ --O).

4-Benzyloxycyclohexanone hydantoin 42

4-Benzyloxycyclohexanone 41 is dissolved in 30 mL of 50% ethanolcontaining ammonium carbonate and potassium cyanide is added (Step 38).The mixture will be warmed to 60° C. for 2 h and evaporated to drynessin vacuo. The residue is extracted with 40 mL of hot methanol, filtered,and the filter cake washed with 20 mL of hot methanol. The methanolsolutions are combined, solvent evaporated, and the residuechromatographed on silica gel using CH₂ Cl₂ /methanol 90:10 to yield 42.

1-Amino-4-benzyloxycyclohexane-1-carboxylic acid 43

The hydantoin 42 is hydrolyzed by refluxing with 10 mL of a bariumhydroxide solution (saturated at room temperature) for 16 h (Step 39).The solution is neutralized to pH 6 with 2N sulfuric acid and evaporatedto dryness in vacuo. The residue is extracted with 50 mL of hotmethanol, filtered, and washed with 50 mL of hot methanol. The methanolsolutions are combined and evaporated.

1-t-Butyl carbamate-3-benzyloxy-1-cyclohexane-1-carboxylic acid 44

A solution of the amino acid in 10 mL of a mixture ofmethanol/triethylamine (90:10) is treated with di-tert-butyl dicarbonate(Step 40). The mixture is heated at 50°-60° C. for 10 min and then thesolvent is removed by rotoevaporation. The crude product is stirred in 5mL of dilute Hcl (pH=2) at 0° C. for 10 min. The mixture is extractedwith CH₂ Cl₂ (2×10 mL), the combined extract dried, and the solventremoved. The crude oil is chromatographed on silica gel using methylenechloride/methanol (9 to 1) with 0.1% formic acid to yield 44.

1-t-Butyl carbamate-3-benzyloxy-1-cyclohexane-1-carboxylic acid methylester 45

To a slurry of 1-methyl-3-nitro-1-nitrosoguandine in ether at 0°-5° C.is added to a 40% solution of potassium hydroxide dropwise. Theresultant diazomethane ether solution is added to 1-t-Butylcarbamate-3-benzyloxy-1-cyclohexane-1-carboxylic acid 44 in 3 mL ofether and the mixture is stirred at room temperature for 15 min (Step41). The mixture is washed with water (10 mL) and the ether evaporated.The crude residue is chromatographed on silica gel using ethylacetate/hexane (1 to 9) to yield 45.

1-t-Butyl carbamate-3-hydroxy-1-cyclobutane-1-carboxylic acid methylester 46

A solution of the protected amino acid benzyl ether 45 in 5 mL ofmethanol is mixed with a suspension of 25 mg of 10% palladium oncharcoal in 5 mL of methanol (Step 42). The mixture is stirred under apositive pressure of hydrogen (balloon) for 16 hr. The catalyst isfiltered off and the solvent is evaporated. The crude residue ischromatographed on silica gel using methylene chloride/methanol (9 to 1)to yield 46.

1-t-Butyl carbamate-3-trifluoromethanesulfonoxy-1-cyclohexane-1-carboxylic acid methyl ester 47

The alcohol 46 is dissolved in 10 mL of dry methylene chloride andpyridine (12 μL) by stirring under N₂. The solution is cooled to 0°-5°C. and 12 μL of trifluoromethane sulfonic anhydride is added (Step 43).After 1 hr, the solvent is removed in vacuo and the crude oil ischromatographed on silica gel using ethyl acetate/hexane (3:7).

¹⁸ F!-1-Amino-3-fluorocyclohexane-1-carboxylic acid 49

¹⁸ F!-Fluoride is produced using the ¹⁸ O(p,n) ¹⁸ F reaction with 11 MeVprotons on 95% enriched ¹⁸ O! water. After evaporation of the water anddrying of the fluoride by acetonitrile evaporation, the protected aminoacid triflate 47 (3 mg) is introduced in an acetonitrile solution (1mL). The (NCA) fluorination reaction is performed at 85° C. for 5 min ina sealed vessel in the presence of potassium carbonate and Kryptofix(Step 44). Unreacted ¹⁸ F⁻ is removed by diluting the reacting mixturewith methylene chloride followed by passage through a silica gel Seppakwhich gives the ¹⁸ F labeled product. Deprotection (Step 45) is achievedby using 1 mL of 4N HCl at 115° C. for 15 min and then the aqueoussolution is passed through an ion-retardation resin (AG 11A8 50-100mesh) to yield FACHC 49.

EXAMPLE 5

¹⁸ F!-1-Amino-3-(fluoromethyl)cyclobutane-1-carboxylic acid 60

Dimethyl ester 3-hydroxycyclobutane-1,1-dicarboxylate 51

To a slurry of 1-methyl-3-nitro-1-nitrosoguandine (150 mg) in 8 mL ofether at 0°-5° C. was added a 40% solution of potassium hydroxidedropwise. The resultant diazomethane ether solution was added to 0.15 g(0.50 mmol) of 50 in 3 mL of ether and the mixture was stirred at roomtemperature for 15 min (Step 46). The mixture was washed with water (10mL) and the ether evaporated. The crude residue was chromatographed onSilica gel.

Dimethyl 3-(benzyloxymethyl)cyclobutane-1,1-dicarboxylate 52

Sodium hydride (60% oil dispersion, 2.1 g, 53 mmol) is added in portionsto a solution of dimethyl 3-(hydroxymethyl)cyclobutane-1,1-dicarboxylate(51), benzyl bromide, and n-tetrabutylammonium iodide in dry DMF at 25°C. (Step 47). The mixture is stirred for 1 hr at 65° C., poured onto iceand then extracted with ether (2×50 mL). The combined ether extract iswashed with water (3×50 mL) and dried over MgSO₄. Chromatography onsilica gel.

18F!-1-Amino-3-(fluoromethyl)cyclobutane-1-carboxylic acid ##STR10##3-(Benzyloxymethyl)cyclobutane-1,1-dicarboxamine 53

Dimethyl 3-(benzyloxymethyl)cyclobutane-1,1-dicarboxylate (52) isstirred with concentrated aqueous ammonia (100 mL) for four days at roomtemperature (Step 48). The resultant diamide is collected by filtrationand washed with water followed by ethyl acetate.

Cis/trans 5-((3-benzyloxymethyl)cyclobutane)hydantoin 54

3-(Benzyloxymethyl)cyclopentane-1,1-dicarboxamine (53) is stirred withdilute sodium hypochlorite (Aldrich product/water 1:2) at 0°-5° C. for 4hr and then allowed to stand overnight at room temperature (Step 49).Unreacted diamide is recovered by filtration. The solution isneutralized to pH 5 with concentrated hydrochloric acid and evaporatedto dryness in vacuo. The residue is extracted with 50 mL of hotmethanol, filtered, and washed with 50 mL of hot methanol. The methanolsolutions are combined and evaporated.

1-Amino-3-(benzyloxymethyl)cyclobutane-1-carboxylic acid 55

The hydantoin 54 is hydrolyzed by refluxing with 10 mL of a bariumhydroxide solution (saturated at room temperature) for 16 hr (Step 50).The solution is neutralized to pH 6 with 2M sulfuric acid and evaporatedto dryness in vacuo. The residue is extracted with 50 mL of hotmethanol, filtered, and washed with 50 mL of hot methanol. The methanolsolutions are combined and evaporated.

1-t-Butyl carbamate-3-(benzyloxymethyl)cyclobutane-1-carboxylicacid

A solution of the amino acid (55) in 10 mL of a mixture ofmethanol/triethylamine (90:10) is treated with di-tert-butyl dicarbonate(Step 51). The mixture is heated at 50°-60° C. for 10 min and then thesolvent is removed by rotoevaporation. The crude product is stirred in 5mL of dilute HCl (pH=2) at 0° C. for 10 min. The mixture is extractedwith CH₂ Cl₂ (2×10 mL), the combined extract dried, and the solventremoved. The crude oil is chromatographed on silica gel using methylenechloride/methanol (9 to 1) with 0.1% formic acid.

1-t-Butyl carbamate-3-(benzyloxymethyl)cyclobutane-1-carboxylicacidmethyl ester 57

To a slurry of 1-methyl-3-nitro-1-nitrosoguandine in ether at 0°-5° C.is added a 40% solution of potassium hydroxide dropwise. The resultantdiazomethane ether solution is added to carboxylic acid 56 in ether andthe mixture is stirred at room temperature for 15 min. (Step 52). Themixture is washed with water and the ether evaporated. The crude residueis chromatographed on silica gel using ethyl acetate/hexane (1 to 9).

1-t-Butyl carbamate-3-(hydroxymethyl)cyclobutane-1-carboxylic acidmethyl ester 58

A solution of the protected amino acid benzyl ether 57 in methanol ismixed with a suspension of 10% palladium on charcoal in 5 mL of methanol(Step 53). The mixture is stirred under a positive pressure of hydrogen(balloon) for 16 hr. The catalyst is filtered off and the solvent isevaporated. The crude residue is chromatographed on silica gel usingmethylene chloride/methanol (9 to 1).

1-t-Butyl carbamate-3-(trifluoromethanesulfonoxymethyl)cyclobutane-1-carboxylic acid methyl ester 59

The alcohol 58 is dissolved in 10 mL of dry methylene chloride andpyridine (12 μL) by stirring under N₂. The solution is cooled to 0°-5°C., and 12 μL of trifluoromethane sulfonic anhydride is added (Step 54).After 1 hr, the solvent is removed in vacuo and the crude oil ischromatographed on silica gel using ethyl acetate/hexane (3:7).

¹⁸ F!-1-Amino-3-(fluoromethyl)cyclobutane-1-carboxylic acid 60

¹⁸ F!-Fluoride is produced using the ¹⁸ O(p,n)¹⁸ F reaction with 11 MeVprotons on 95% enriched ¹⁸ O! water. After evaporation of the water anddrying of the fluoride by acetonitrile evaporation, the protected aminoacid triflate 58 (3 mg) is introduced in an acetonitrile solution (1mL). The (NCA) fluorination reaction is performed at 85° C. for 5 min ina sealed vessel in the presence of potassium carbonate and Kryptofix(Step 55). Unreacted ¹⁸ F⁻ is removed by diluting the reacting mixturewith methylene chloride followed by passage through a silica gel Seppakwhich gives the ¹⁸ F labeled product. Deprotection of 59 is achieved byusing 1 mL of 4N HCl at 115° C. for 15 min (Step 56) and then aqueoussolution is passed through an ion-retardation resin (AG 11A8 50-100mesh).

EXAMPLE 6

Synthesis of ¹²³ I!-1-Amino-3-iodocyclobutane-1-carboxylic acid 61

¹²³ I!-Sodium iodide (10 mCi, 0.1N NaOH solution) is dried byacetonitrile (2 mL) evaporation, the protected amino acid triflate 11 (3mg) is introduced in an acetonitrile solution (1 mL) (Step 57). The(NCA) iodination reaction is performed at 85° C. for 5 min in a sealedvessel. Unreacted ¹⁸ F⁻ is removed by diluting the reacting mixture withmethylene chloride followed by passage through a silica gel Seppak whichgives the ¹⁸ I labeled product. Deprotection is achieved by using 1 mLof 4N HCl at 115° C. for 15 min (Step 58) and then the aqueous solutionis passed through an ion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 7

Synthesis of ¹²³ I!-1-Amino-3-iodocyclobut-2-ene-1-carboxylic acid 65

1-t-Butyl carbamate-3-oxo-1-cyclobutane-1-carboxylic acid methyl ester62

The protected alcohol 10 is added to a suspension of pyridiniumchlorochromate in DMF at 25° C., stirred at 65° C. for 3 h, and thendiluted with water (75 mL) (Step 59). The mixture is extracted withether (2×50 mL) and the combined ether layers were washed with water,dried (MgSO4) and the solvent removed by roto-evaporation.

1-t-Butyl carbamate-1-cyclobutane-1-carboxylic acid methyl ester!3-hydrazone 63

A mixture of hydrazine, ketone 62, DBN, and 20 mL of ethanol is heatedto boiling (Step 60). The mixture is kept hot for 10 min. The solutionis cooled, and the hydrazone is collected by filtration.

₁₂₃ I!-1-Amino-3-iodo-cyclobut-2-ene-1-carboxylic acid 65

Aqueous 3% hydrogen peroxide is added to a mixture of sodium ₁₂₃I!iodide, hydrazone 63, and 0.1N HCl in a sealed vial protected by acharcoal vent (Step 61). The reaction is allowed to proceed for

123I!-1-Amino-3-iodocyclobutane-1-carboxylic acid ##STR11##123I!-1-Amino-3-iodocyclobut-2-ene-1-carboxylic acid ##STR12## 30 min atambient temperature, quenched with a solution of sodium bisulfite (300mg/mL). Deprotection of 64 (Step 62) is achieved by using 1 mL of 4N HClat 115° C. for 15 min and then the aqueous solution is passed through anion-retardation resin (AG 11A8 50-100 mesh). EXAMPLE 8

Synthesis of E- ¹²³ I!-1-Amino-3-(2-iodoethenyl)cyclobutane-1-carboxylicacid 69

1-t-Butyl carbamate-3-bromo-1-cyclobutane-1-carboxylic acid methyl ester66

Bromine is added to a mixture of alcohol 10 and triphenylphosphine inDMF at -10° C. (Step 63). After stirring for 1 h, the mixture is dilutedwith water and extracted with ether. The ether layer is washed withwater, 10% sodium sulfite, and then dried. The ether is removed and theresidue is chromatographed on silica gel.

1-t-Butyl carbamate-3-ethynyl-1-cyclobutane-1-carboxylic acid methylester 67

The bromo compound 66 in THF is added to a suspension of lithiumacetylide ethylenediamine complex in THF stirred at 0° C. under anitrogen atmosphere (Step 64). The mixture is stirred for 3 h at 25° C.,poured into ice water, and extracted with ether. The ether extract iswashed with ice cold 1N HCl, brine and then dried. The ether is removedand the residue is chromatographed on silica gel.

1-t-Butylcarbamate-3-((E)-2-tributylstannylethenyl)-1-cyclobutane-1-carboxylicacid methyl ester 68

Tributyltin hydride, the alkyne 67 and azobisisobutyronitrile arerefluxed in toluene under nitrogen atmosphere for 10 h (Step 65). Thereaction mixture is cooled, solvent removed in vacuo, and the residuechromatographed on silica gel.

¹²³ I!-1-Amino-3-((E)-2-iodoethenyl)cyclobut-2-ene-1-carboxylic acid 69

Aqueous 3% hydrogen peroxide is added to a mixture of sodium ¹²⁵I!iodide, tributylstannyl 68, and 0.1N HCl in a sealed vial protected bya charcoal vent (Step 66). The reaction is allowed to

123I!-1-Amino-3-(2-iodoethenyl)cyclobutane-1-carboxylic acid ##STR13##123I!-1-Amino-3-(iodomethylenyl)cyclobutane-1-carboxylic acid ##STR14##proceed for 30 min at ambient temperature, quenched with a solution ofsodium bisulfite (300 mg/mL). Deprotection (Step 67) is achieved byusing 1 mL of 4N HCl at 115° C. for 15 min and then the aqueous solutionis passed through an ion-retardation resin (AG 11A8 50-100 mesh).EXAMPLE 9

Synthesis of ¹²³ I!-1-Amino-3-(iodomethylenyl)cyclobutane-1-carboxylicacid

(Bromomethyl)triphenylphosphonium bromide 70

A mixture of hydroxymethyl)triphenylphosphonium bromide and phosphorustribromide in benzene is heated at reflux for 23 h with stirring. Afterthis time the solution is dark orange and an orange solid is present Themixture is cooled to 25° C. and methanol is added. The solvent wasremoved at reduced pressure and the residue treated with water toextract the phosphonium salt. The aqueous extracts were saturated withsolid potassium bromide and extracted with chloroform. The phosphoniumsalts are crystallized from hot chloroform by addition of ethyl acetate.

1-t-Butyl carbamate-3-(bromomethylenyl)-1-cyclobutane-1-carboxylic acidmethyl ester 71

The phosphonium salt 70 is suspended in ether and ethereal phenyllithiumis added rapidly at 25° C. An orange-yellow solution results whichbecomes mustard yellow within 2 h. To this solution is added protectedketone 62 and the reaction mixture is heated at reflux for 8 h withstirring (Step 68). The ether is removed and the residue ischromatographed on silica gel.

1-t-Butylcarbamate-3-(tributylstannylmethylenyl)-1-cyclobutane-1-carboxylic acidmethyl ester 72

To a solution of 71 in ether at -78° C. is added t-butyllithium (2 eq.)after 15 min tributyltin chloride is added and the mixture is warmed to25° C. (Step 69). The reaction mixture is poured into ice water and theether layer separated and dried. The ether is removed and the residue ischromatographed on silica gel.

¹²³ I!-1-Amino-3-(iodomethylenyl)cyclobutane-1-carboxylic acid 74

Aqueous 3% hydrogen peroxide is added to a mixture of sodium ¹²⁵I!iodide, tributylstannyl 72, and 0.1N HCl in a sealed vial protected bya charcoal vent (Step 70). The reaction is allowed to proceed for 30 minat ambient temperature, quenched with a solution of sodium bisulfite(300 mg/mL). Deprotection of 73 (Step 71) is achieved by using 1 mL of4N HCl at 115° C. for 15 min and then the aqueous solution is passedthrough an ion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 10

¹²³ I!-2-Amino-2-methyl-4-(E)-iodobut-3-en-1-oic acid

2-t-Butyl carbamate-2-methyl-3-carbomethoxy propanol 75

The protected alcohol 22 is added to a suspension of pyridiniumchlorochromate in DMF at 25° C., stirred at 65° C. for 3 h, and thendiluted with water (75 mL) (Step 72). The mixture is extracted withether (2×50 mL) and the combined ether layers were washed with water,dried (MgSO₄) and the solvent removed by roto-evaporation.

2-t-Butyl carbamate-2-methyl-4-(E)-bromobut-3-en-1-oic acid methyl ester76

The phosphonium salt 70 is suspended in ether and ethereal phenyllithiumis added rapidly at 25° C. An orange-yellow solution results whichbecomes mustard yellow within 2 h. To this solution is added protectedaldehyde 75 and the reaction mixture is heated at reflux for 8 h withstirring (Step 73). The ether is removed and the residue ischromatographed on silica gel.

2-t-Butyl carbamate-2-methyl-4-(E)-tributylstannylbut-3-en-1-oic acidmethyl ester 77

To a solution of 76 in ether at -78° C. will be added t-butyllithium (2eq.) after 15 min tributyltin chloride is added and the mixture iswarmed to 25° C. (Step 74). The reaction mixture is poured into icewater and the ether layer separated and dried. The ether is removed andthe residue is chromatographed on silica gel.

Synthesis of 123I!-2-Amino -2-methyl-4-(E)-iodobut-3-en-1-oic acid##STR15## ¹²³ I!-2-Amino-2-methyl-4-(E)-iodobut-3-en-1-oic acid 79

Aqueous 3% hydrogen peroxide is added to a mixture of sodium ¹²³I!iodide, tributylstannyl 77, and 0.1N HCl in a sealed vial protected bya charcoal vent (Step 75). The reaction is allowed to proceed for 30 minat ambient temperature, quenched with a solution of sodium bisulfite(300 mg/mL). Deprotection of 78 (Step 76) is achieved by using 1 mL of4N HCl at 115° C. for 15 min and then the aqueous solution is passedthrough an ion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 11

Synthesis of ¹²³ I!-1-Amino-3-iodocyclopentane-1-carboxylic acid 80

¹²⁵ I!-Sodium iodide (10 mCi, 0.1N NaOH solution) is dried byacetonitrile (2 mL) evaporation, the protected amino acid triflate 35 (3mg) is introduced in an acetonitrile solution (1 mL). The (NCA)iodination reaction is performed at 85° C. for 5 min in a sealed vessel.Unreacted ¹²³ I is removed by diluting the reacting mixture withmethylene chloride followed by passage through a silica gel Seppak whichgives the ¹²³ I labeled product. Deprotection is achieved by using 1 mLof 4N HCl at 115° C. for 15 min and then the aqueous solution is passedthrough an ion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 12

Synthesis of ¹²³ I!-1-Amino-3-iodocyclopent-2-ene-1-carboxylic acid

1-t-Butyl carbamate-3-oxo-1-cyclopentane-1-carboxylic acid methyl ester81

The protected alcohol 34 will be added to a suspension of pyridiniumchlorochromate in DMF at 25° C., stirred at 65° C. for 3 h, and thendiluted with water (75 mL) (Step 77). The mixture is extracted withether (2×50 mL) and the combined ether layers are washed with water,dried (MgSO₄) and the solvent removed by roto-evaporation.

123I!-1-Amino-3-iodocyclopentane-1 -carboxylic acid X=1123I!-1-Amino-4-iodocyclohexane-1-carboxylic acid X=2 ##STR16##123I!-1-Amino-3-iodocycopentane-1-carboxylic acid X=1123I!-1-Amino-4-iodocyclohex-2-ene-1-carboxylic acid X=2 ##STR17##1-t-Butyl carbamate-1-cyclopentane-1-carboxylic acid methyl ester!3-hydrazone 82

A mixture of hydrazine, the ketone 81, DBN, and 20 mL of ethanol isheated to boiling (Step 78). The mixture is kept hot for 10 min. Thesolution is cooled, and the hydrazone is collected by filtration.

¹²³ I!-1-Amino-3-iodo-cyclopent-2-ene-1-carboxylic acid 84

Aqueous 3% hydrogen peroxide will be added to a mixture of sodium ¹²³I!iodide, hydrazone 82, and 0.1N HCl in a sealed vial protected by acharcoal vent (Step 79). The reaction is allowed to proceed for 30 minat ambient temperature, quenched with a solution of sodium bisulfite(300 mg/mL). Deprotection of 83 (Step 80) is achieved by using 1 mL of4N HCl at 115° C. for 15 min and then the aqueous solution is passedthrough an ion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 13

Synthesis of E- ¹²³I!-1-Amino-3-(2-iodoethenyl)cyclopentane-1-carboxylic acid 88

1-t-Butyl carbamate-3-bromo-1-cyclopentane-1-carboxylic acid methylester 85

Bromine is added to a mixture of alcohol 34 and triphenylphosphine inDMF at -10° C. (Step 81). After stirring for 1 h, the mixture is dilutedwith water and extracted with ether. The ether layer is washed withwater, 10% sodium sulfite, and then dried. The ether is removed and theresidue is chromatographed on silica gel.

1-t-Butyl carbamate-3-ethynyl-1-cyclopentane-1-carboxylic acid methylester 86

The bromo compound 85 in THF is added to a suspension of lithiumacetylide ethylenediamne complex in THF stirred at 0° C. under anitrogen atmosphere (Step 82). The mixture is stirred for 3 h at 25° C.,poured into ice water, and extracted with ether. The ether extract iswashed with ice cold 1N HCl, brine and then dried. The ether is removedand the residue is chromatographed on silica gel.

E- 123I!-1-Amino-4-(2-iodoethenyl)cyclopentane-1-carboxylic acid X=1 E-1231!-1-Amino-4-(2-iodoethenyl)cyclohexane-1-carboxylic acid X=2##STR18## 123I!-Amino-3-(iodomethylenylcyclopentane-1-carboxylic acidX=1 123I!-1-Amino-4-(iodomethylenyl)cyclohexane-1-carboxylic acid X=2##STR19##1-t-Butylcarbamate-3-((E)-2-tributylstannylethenyl)-1-cyclopentane-1-carboxylicacid methyl ester 87

Tributyltin hydride, the alkyne 86 and azobisisobutyronitrile will berefluxed in toluene under nitrogen atmosphere for 10 h (Step 83). Thereaction mixture is cooled, solvent removed in vacuo, and the residuechromatographed on silica gel.

¹²³ I!-1-Amino-3-((E)-2-iodoethenyl)cyclopentane-1-carboxylic acid 88

Aqueous 3% hydrogen peroxide is added to a mixture of sodium ¹²³I!iodide, tributylstannyl 87, and 0.1N HCl in a sealed vial protected bya charcoal vent (Step 84). The reaction is allowed to proceed for 30 minat ambient temperature, quenched with a solution of sodium bisulfite(300 mg/mL). Deprotection (Step 85) is achieved by using 1 mL of 4N HClat 115° C. for 15 min and then the aqueous solution is passed through anion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 14

Synthesis of ¹²³ I!-1-Amino-3-(iodomethylenyl)cyclopentane-1-carboxylicacid 93

1-t-Butyl carbamate-3-(bromomethylenyl)-1-cyclopentane-1-carboxylic acidmethyl ester 90

The phosphonium salt 70 is suspended in ether and ethereal phenyllithiumis added rapidly at 25° C. An orange-yellow solution results whichbecomes mustard yellow within 2 h. To this solution is added protectedketone 81 and the reaction mixture is heated at reflux for 8 h withstirring (Step 86). The ether is removed and the residue ischromatographed on silica gel.

1-t-Butylcarbamate-3-(tributylstannylmethylenyl)-1-cyclopentane-1-carboxylic acidmethyl ester 91

To a solution of 90 in ether at -78° C. is added t-butyllithium (2 eq.)after 15 min tributyltin chloride is added and the mixture is warmed to25° C. (Step 87). The reaction mixture is poured into ice water and theether layer separated and dried. The ether is removed and the residue ischromatographed on silica gel.

¹²³ I!-1-Amino-3-(iodomethylenyl)cyclopentane-1-carboxylic acid 93

Aqueous 3% hydrogen peroxide is added to a mixture of sodium ¹²³I!iodide, tributylstannyl 91, and 0.1N HCl in a sealed vial protected bya charcoal vent (Step 88). The reaction is allowed to proceed for 30 minat ambient temperature, quenched with a solution of sodium bisulfite(300 mg/mL). Deprotection of 92 (Step 89) is achieved by using 1 mL of4N HCl at 115° C. for 15 min and then the aqueous solution is passedthrough an ion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 15

Synthesis of ¹²³ I!-1-Amino-4-iodocyclohexane-1-carboxylic acid 94

¹²³ I!-Sodium iodide (10 mCi, 0.1N NaOH solution) will be dried byacetonitrile (2 mL) evaporation, the protected amino acid triflate 46 (3mg) is introduced in an acetonitrile solution (1 mL). The (NCA)iodination reaction is performed at 85° C. for 5 min in a sealed vessel.Unreacted ¹²³ I is removed by diluting the reacting mixture withmethylene chloride followed by passage through a silica gel Seppak whichgives the ¹²³ I labeled product. Deprotection is achieved by using 1 mLof 4N HCl at 115° C. for 15 min and then the aqueous solution is passedthrough an ion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 16

Synthesis of ¹²³ I!-1-Amino-4-iodocyclohex-2-ene-1-carboxylic acid

1-t-Butyl carbamate-4-oxo-1-cyclohexane-1-carboxylic acid methyl ester95

The protected alcohol 46 is added to a suspension of pyridiniumchlorochromate in DMF at 25° C., stirred at 65° C. for 3 h, and thendiluted with water (75 mL) (Step 77). The mixture is extracted withether (2×50 mL) and the combined ether layers are washed with water,dried (MgSO4) and the solvent removed by roto-evaporation.

1-t-Butyl carbamate-1-cyclohexane-1-carboxylic acid methyl ester!4-hydrazone 96.

A mixture of hydrazine, the ketone 95, and 20 mL of ethanol is heated toboiling, and a drop of glacial acetic acid is added. The mixture is kepthot for 10 min (Step 78). The solution is cooled, and the hydrazone iscollected by filtration.

¹²³ I!-1-Amino-4-iodo-cyclohex-2-ene-1-carboxylic acid 98

Aqueous 3% hydrogen peroxide is added to a mixture of sodium ¹²⁵I!iodide, hydrazone 96, and 0.1N HCl in a sealed vial protected by acharcoal vent (Step 79). The reaction is allowed to proceed for 30 minat ambient temperature, quenched with a solution of sodium bisulfite(300 mg/mL). Deprotection of 97 (Step 80) is achieved by using 1 mL of4N HCl at 115° C. for 15 min and then the aqueous solution is passedthrough an ion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 17

Synthesis of E- ¹²³ I!-1-Amino-3-(2-iodoethenyl)cyclohexane-1-carboxylicacid

1-t-Butyl carbamate-4-bromo-1-cyclohexane-1-carboxylic acid methyl ester99

Bromine is added to a mixture of alcohol 46 and triphenylphosphine inDMF at -10° C. (Step 81). After stirring for 1 h, the mixture is dilutedwith water and extracted with ether. The ether layer is washed withwater, 10% sodium sulfite, and then dried. The ether is removed and theresidue is chromatographed on silica gel.

1-t-Butyl carbamate-4-ethynyl-1-cyclohexane-1-carboxylic acid methylester 100

The bromo compound 99 in THF is added to a suspension of lithiumacetylide ethylenediamne complex in THF stirred at 0° C. under anitrogen atmosphere (Step 82). The mixture is stirred for 3 h at 25° C.,poured into ice water, and extracted with ether. The ether extract iswashed with ice cold 1N HCl, brine and then dried. The ether is removedand the residue is chromatographed on silica gel.

1-t-Butylcarbamate-4-((E)-2-tributylstannylethenyl)-1-cyclohexane-1-carboxylicacid methyl ester 101

Tributyltin hydride, the alkyne 100 and azobisisobutyronitrile arerefluxed in toluene under nitrogen atmosphere for 10 h (Step 83). Thereaction mixture is cooled, solvent removed in vacuo, and the residuechromatographed on silica gel.

¹²³ I!-1-Amino-4-((E)-2-iodoethenyl)cyclohexane-1-carboxylic acid 102

Aqueous 3% hydrogen peroxide is added to a mixture of sodium ¹²³I!iodide, tributylstannyl 101, and 0.1N HCl in a sealed vial protectedby a charcoal vent (Step 84). The reaction is allowed to proceed for 30min at ambient temperature, quenched with a solution of sodium bisulfite(300 mg/mL). Deprotection (Step 85) is achieved by using 1 mL of 4N HClat 115° C. for 15 min and then the aqueous solution is passed through anion-retardation resin (AG 11A8 50-100 mesh).

EXAMPLE 18

Synthesis of ¹²³ I!-1-Amino-4-(iodomethylenyl)cyclohexane-1-carboxylicacid

1-t-Butyl carbamate-4-(bromomethylenyl)-1-cyclohexane-1-carboxylic acidmethyl ester 103

The phosphonium salt 70 is suspended in ether and ethereal phenyllithiumis added rapidly at 25° C. An orange-yellow solution results whichbecomes mustard yellow within 2 h. To this solution is added protectedketone 95 and the reaction mixture is heated at reflux for 8 h withstirring (Step 86). The ether is removed and the residue ischromatographed on silica gel.

1-t-Butylcarbamate-4-(tributylstannylmethylenyl)-1-cyclohexane-1-carboxylic acidmethyl ester 104

To a solution of 103 in ether at -78° C. is added t-butyllithium (2 eq.)after 15 min tributyltin chloride is added and the mixture is warmed to25° C. (Step 87). The reaction mixture is poured into ice water and theether layer separated and dried. The ether is removed and the residue ischromatographed on silica gel.

¹²³ I!-1-Amino-4-(iodomethylenyl)cyclohexane-1-carboxylic acid 106

Aqueous 3% hydrogen peroxide will be added to a mixture of sodium125I!iodide, tributylstannyl 104, and 0.1N HCl in a sealed vialprotected by a charcoal vent (Step 88). The reaction is allowed toproceed for 30 min at ambient temperature, quenched with a solution ofsodium bisulfite (300 mg/mL). Deprotection of 105 (Step 89) is achievedby using 1 mL of 4N HCl at 115° C. for 15 min and then the aqueoussolution is passed through an ion-retardation resin (AG 11A8 50-100mesh).

EXAMPLE 19

Biodistribution Studies in Tumor Bearing Rats

The distribution of radioactivity expressed as percent dose per gram intissues of unfasted male fisher rats with implanted gliosarcoma at 5 minand 60 min after intravenous administration of ¹⁸ F!FACBC is shown inTable I. The initial level of accumulation of radioactivity in the brainafter injection of ¹⁸ F!FACBC was low (0.11% dose/gram) at 5 min andincreased slightly to 0.26% dose/gram. The agent, however, exhibited ahigh uptake in the brain tumor. The tumor uptake exhibited a maximum at60 min (1.72% dose/gram) resulting in an increase in the tumor to brainratio of 5.58 at 5 min to 6.61 at 60 min. The bone radioactivity showedno increase from 0.52% dose/gram at 5 min, to 0.38% dose/gram at 60 min,which demonstrates the expected stability of the 2-cyclobutyl group tosignificant in vivo defluorination.

We compared the tumor uptake of ¹⁸ F!FACBC with ¹⁸ F!2-FDG in a separategroup of male fisher rats with implanted gliosarcoma at 5 min and 60 minafter intravenous administration of ¹⁸ F!2-FDG the initial level ofaccumulation of radioactivity in the brain tumor after injection of ¹⁸F!2-FDG was good, 1.29% dose/gram. The 2-FDG, however, exhibited adecrease in uptake in the brain tumor to 1.05% dose/gram at 60 min. Thedecrease of radioactivity in the tumor at 60 min in conjunction withinitial high brain uptake and retention resulted in a low tumor to brainratio of 0.84 at 60 min.

                  TABLE I                                                         ______________________________________                                        Distribution of Radioactivity in Tissues of Unfasted Male                     Fisher Rats following Intravenous Administration of  .sup.18 F!FACBC                      Mean % Injected Dose/Gram                                                     (Average of 4 Rats)                                               Organ         5 min     60 min                                                ______________________________________                                        Blood         0.58      0.32                                                  Heart         0.70      0.56                                                  Muscle        0.27      0.41                                                  Lung          1.13      0.64                                                  Kidney        1.08      0.60                                                  Spleen        1.55      0.68                                                  Liver         1.10      1.70                                                  Testis        0.25      0.28                                                  Bone          0.52      0.38                                                  Brain (B)     0.11      0.26                                                  Tumor (T)     0.61      1.72                                                  T/B           5.58      6.61                                                  ______________________________________                                    

This significant tumor to brain ratio of 6.6 at 60 min strongly supportsthe use of ¹⁸ F!FACBC as a valuable imaging agent for the diagnosis andmanagement of treatment of metastatic disease in humans by PET.

We claim:
 1. An amino acid analog having the general structure ##STR20##where R₁ is X, X--CH═CH--, or R₃ R₂ is H, or R₃ if R₁ is R₃, ##STR21##such that ##STR22## is formed where x is 0 or 1,y is 1 or 2, z is 1, 2,3 or 4 and z>y if y is 2, q is 1 or 0 if n is 1 and j is 0, n is 1 or 2,but 0 if m is 0, m is 0 or 1, j is 0 or 1, and X is ¹⁸ F, ¹²³ I, ¹²⁵ I,¹³¹ I, ⁷⁵ Br, ⁷⁶ Br, ⁷⁷ Br, or ⁸² Br.
 2. A compound of claim 1, whereinR₁ and R₂ =R₃.
 3. A cyclic compound according to claim 1 whereinx is 0 yis 1 z is 2 q is 1 m is 0, and j is
 0. 4. A compound according to claim3 wherein X is ¹⁸ F, or ¹²³ I.
 5. A compound according to claim 3wherein X is ¹⁸ F.
 6. A compound according to claim 1 wherein R₁ and R₂=R₃,x is 0 or 1 y is 2 z is 4 q is 1 m and j are each 0, and X is ¹⁸ F,or ¹²³ I.
 7. A compound according to claim 6 whereinx is 1 X is ¹⁸ F. 8.The compound of claim 8 wherein x is 0 and X is ¹²³ I.
 9. A compoundaccording to claim 6 wherein x is 1 and X is ¹²³ I.
 10. A compoundaccording to claim 1wherein R₁ and R₂ =R₃ x is 0 y is 1 z is 2 q is 0 mis 1 n is 1 j is 0, and X is ¹⁸ F, or ¹²³ I.
 11. A compound according toclaim 10 wherein X is ¹⁸ F.
 12. A compound according to claim 1whereinR₁ and R₂ =R₃ x is 1 y is 1 z is 1 q is 0 m and j are 0, and X is ¹⁸ F,or ¹²³ I.
 13. A compound according to claim 12 wherein X is ¹²³ I.
 14. Acompound according to claim 1wherein R₁ and R₂ =R₃ x is 0 y is 1 z is 2q is 1 m is 1 n is 1 j is 1, and X is ¹⁸ F, or ¹²³ I.
 15. The compoundof claim 14 wherein X is ¹²³ I.
 16. A compound according to claim1wherein R₁ and R₂ =R₃ x is 0 y is 1 z is 2 q is 0 m is 0 j is 1, and Xis ¹⁸ F, or ¹²³ I.
 17. The compound of claim 16 wherein X is ¹²³ I. 18.A compound according to claim 1wherein R₁ and R₂ =R₃ x is 0 or 1 y is 2z is 4 q is 1 m is 1 n is 1 j is 1, and X is ¹⁸ F, or ¹²³ I.
 19. Thecompound of claim 18 wherein X is ¹⁸ F.
 20. The compound of claim 18wherein X is ¹²³ I.
 21. A compound according to claim 1wherein R₁ and R₂=R₃ x is 0 or 1 y is 2 z is 4 q is 0 m is 0 j is 1, and X is ¹⁸ F, or¹²³ I.
 22. The compound of claim 21 wherein X is ¹⁸ F.
 23. The compoundof claim 21 wherein X is ¹²³ I.
 24. A compound of claim 1 wherein R₁ andR₂ ≠R₃.
 25. A compound according to claim 24 wherein X is ¹⁸ F.
 26. Acompound according to claim 1 wherein R₁ is X--CH═CH--, R₂ is H, y is 1and z is
 2. 27. A compound of claim 26 wherein X is ¹²³ I.